Referring to FIG. 19, slots b of the illustrated type of conventional slot array antenna for a radar system are formed within a side plate of the waveguide a. The electromagnetic waves fed to the waveguide a radiate from the slots. The ratio X:Y of the width X to the height Y of the waveguide is approximately 2:1.
Within a waveguide for a TE mode wave which requires a large gain, a plurality of waveguides are disposed in parallel with respect to each other.
However, in such a slot array antenna, the construction of the waveguide becomes complicated. Since the inner surface area of each waveguide increases, the propagation loss increases and the weight thereof also increases.